Several industrial processes require hot water in the range of 60-80° C. for heating applications, like paint booth in automobile industry, paper industry, food industry, hotels, and the like. Extensive amount of energy is consumed during the heating application, which adds to the operating costs of the process. Generally, the energy sources used for heating water are fossil fuels including natural gas, liquefied petroleum gas, oil, or solid fuels. These fuels may be consumed directly or by the use of electricity, which may be derived from the above mentioned energy sources. Alternatively, hot water can be generated using solar energy, heat pumps, hot water heat recycling or geothermal heating. The hot water thus generated is sent to the application point where it loses the heat and is then recycled to the hot water generating system.
These industries also require chilled water/refrigeration for the various process applications. Refrigeration is commonly used in industries to liquefy gases like oxygen, nitrogen, propane and methane; in compressed air purification to condense water vapor from compressed air to reduce its moisture content; in oil refineries, chemical plants and petrochemical plants to maintain a low process temperature; and metallurgy industries to temper steel and cutlery. The chiller apparatus commonly used in industrial operations are based on a vapor compression or a vapor absorption cycle. Absorption chiller apparatus are thermally driven, which means that heat rather than mechanical energy is supplied to drive the cycle. Further, absorption chiller apparatus for space conditioning are often gas-fired, while industrial installations are usually driven by high-pressure steam or waste heat. The absorption systems utilize the ability of liquids or salts to absorb vapors of a working fluid to obtain the heating and the cooling effect.
The vapor compression cycle uses high grade energy from mechanical inputs while the vapor absorption cycle uses energy input from waste heat or heat derived from solar collectors. Thus, vapor absorption machines substantially reduce the operating costs as they use low-grade waste heat. Also, the vapor absorption systems use non-ozone depleting refrigerants (water) and require much lesser electricity compared to the vapor compression systems. These systems are even more beneficial for industrial applications where waste heat can be used to generate steam/hot water.
The awareness and need for energy conservation has highlighted concerns about the environment, leading to increase in research and development of energy efficient heating and cooling systems. Increased attention has been directed towards development of cost-effective and efficient systems that can provide heating and cooling, thus, reducing the consumption of energy. As a result, the vapor absorption systems are gaining favor over conventional vapor compression systems in industrial applications, as they use little energy and are environmental friendly.
The basic vapor absorption cycle employs two fluids, the refrigerant and the absorbent. Most commonly, lithium bromide (Li—Br)—water are used as the absorbent-refrigerant pair. In the absorption cycle the low-pressure refrigerant vapor is absorbed into the absorbent releasing a large amount of heat. The liquid refrigerant/absorbent solution is pumped to a high-operating pressure generator, where heat is provided from a gas burner, steam, hot water or hot gases. The heat causes the refrigerant to be desorbed from the absorbent and vaporize. These vapors flow to a condenser, where the heat is rejected and the refrigerant is condensed to liquid refrigerant. The liquid refrigerant is then passed to a low-pressure evaporator, where it evaporates by absorbing heat from chilled water flowing through its tubes and providing the cooling effect. The absorbent in the generator after desorbing refrigerant vapors is sent to absorber where it is recombined with the low-pressure refrigerant vapors returning from the evaporator, repeating the cycle. These systems utilize heat source such as steam, hot water or hot gases leaving a boiler, turbine or engine generators.
A vapor absorption chiller heater apparatus is a system wherein the vapor absorption technology can be used to obtain both hot water and refrigeration effect simultaneously. With stringent pollution control regulations, application of chiller heater apparatus in industries has become important, since the technology helps to reduce emissions, improves efficiency, and limits the use of ground water for cooling.
Several attempts have been made for providing a vapor absorption chiller heater which provides simultaneous heating and refrigeration effect. Some of these disclosures are listed in the prior art below:
Accordingly, U.S. Pat. No. 4,290,273 discloses a chiller and heat pump system employing the Peltier effect in which a steam-jet refrigeration unit is associated with a condenser and an evaporator absorption unit. Peltier effect absorption is conducted thermo-electrically and separately discharges high temperature water and strong absorbent liquid. The high pressure water is passed through a flash chamber for conversion to steam and to reduce its temperature and pressure values to those required for the steam-jet refrigeration unit. The high temperature strong absorbent is passed through a heat exchanger so as to recover heat into the weak absorbent feed to the generator. The steam-jet refrigeration unit separately discharges high temperature steam passed through the condenser means to change its condition to liquid and to transfer heat into a space heating circuit when desired. During simultaneous heating and cooling mode, the chiller and heat pump system disclosed in U.S. Pat. No. 4,290,273A cannot produce temperature required for industrial application. The chiller and heat pump system disclosed in U.S. Pat. No. 4,290,273A is complicated in construction and requires valves for diverting the flow of the absorbent liquid using temperature sensors.
Again, U.S. Pat. No. 4,505,123 discloses an absorption heat pump system having a generator, a condenser, an evaporator and an absorber connected hermetically to form closed cycles for a refrigerant and an absorbent. A control means is disposed in the refrigerant passage leading from the condenser to the evaporator and is adapted to continuously control the temperature or flow rate of the liquid refrigerant, so as to stabilize the temperature in the evaporator. The control means of U.S. Pat. No. 4,505,123 require a liquid refrigerant heater in heat exchanging relation with the refrigerant passage for heating the refrigerant. The requirement of a refrigerant heater increases the cost of the system.
Again, WO 1994017343 discloses a heat pump and refrigeration system including an evaporator from which refrigerant vapour is withdrawn by an absorber and an absorbent is recharged by a generator. Further, a condenser is provided between the generator and the evaporator so that refrigerant vapour from the generator can be condensed prior to being returned to the evaporator. In addition, the system is provided with an ejector which is positioned downstream of the evaporator so as to withdraw refrigerant vapour from same and upstream of the condenser so that said withdrawn refrigerant vapour passes through the ejector to the condenser. The use of the ejector complicates the circulation of the refrigerant vapour to the absorber and also adds to the cost of the system. The system disclosed in WO 1994017343 cannot be used to produce high temperature for industrial application
Therefore, there is felt a need for a vapor absorption chiller-heater apparatus that minimizes or eliminates one or more of the shortcomings listed in the prior art above.